For water treatment systems running in acidic or poorly buffered neutral solutions, anodes which are stable in acid are required. Such stable anodes are typically fabricated as active coatings on a corrosion resistant valve metal substrate (for example, but not limited to: titanium, tantalum, and zirconium. See, for example, G. P. Vercesi, J. Rolewicz, Ch. Comninellis, E. Plattner, and J. Hinden, “Characterization of DSA-Type Oxygen Evolving Electrodes. Choice of Base Metal”, Thermochimica Acta, vol. 176, pp. 31–47, (1991). The coatings used (for example, but not limited to: platinum, iridium dioxide, mixed platinum and iridium dioxide, doped tin dioxide, lead dioxide (with and without doping), and doped diamond) are expensive. Therefore it is important when using such anodes, that the cell design ensures that the entire electrode area is effectively used in order to minimise the electrode area required to treat a given volume of contaminated water. Specifically this means that one desires a design that allows for a high and even current density from the anode, and a corresponding high and even mass transport to deliver the solution contaminants to the anode surface at a sufficient rate. It should be understood, however, that while this design provides the greatest advantage with expensive electrode materials such as those described above, it still also provides some advantage for applications with lower cost electrodes (anodes or cathodes) and/or in alkaline solutions.
To treat solutions with low concentrations of contaminants requires good mass transport to deliver the contaminants to the electrode surface. Mass transport is proportional to momentum transport and therefore linked to pressure drop. Thus a cell with high rates of mass transport will also have a high pressure drop. A good cell design must therefore be able to operate with high inlet pressures, and to cause little or no “non-useful” pressure drops in the cell inlet and outlet to avoid wasting pump power. In other words, ideally all the cell pressure drops would be “useful”; due to the interaction of the fluid flow with the working electrodes (i.e. the electrodes at which the desired reaction or reactions are occurring). In order to operate with a high inlet pressure while being inexpensive to fabricate, a cell design must have minimal openings and gaskets, which might leak at high pressure. In order to minimise “non-useful” pressure drops the cell inlet and outlet must avoid abrupt changes in flow velocity or direction (i.e. minimal flow constrictions or corners).
As well as minimising the electrode area required to treat a given volume of contaminated water, the design should also minimise the cell size to minimise the fabrication costs. This requires maximising the electrode area per cell volume. Thus the goal of this cell design is to provide the cheapest possible system while retaining optimal performance.